Public key cryptography technology is known as one of cipher technologies. In this technology, for example, as shown in FIG. 14 in JP-A No. 21057/1998, a sender forms cipher text C through encoding by “C=Me mod N” for a message M, and a receiver obtains the message M through decoding by “M=Cd mod N” for the cipher text C. The parameters e and N in the encoding are publicized and d in the decoding is not publicized. The operational expressions for the encoding and the decoding are power remainder computations (modular exponentiation), and can be typically described as “XY mod N” (X, Y, N are positive integers). “mod” denotes a remainder computation, and the power remainder computation “XY mod N” means that a remainder produced by dividing XY by N is a solution.
In AV (audio-visual) equipment having an IC card and copyright management function, and information equipment or communication devices having cipher processing functions such as a storage device, it is common to provide dedicated hardware to perform cipher processing with high performance and low power consumption. In such equipment, plural different cipher processings must be performed according to the use and object of application software, and an encryption system of digital contents, and a single device often includes plural pieces of cipher processing hardware.
As a method for achieving identical cipher processing with different logical configurations, with respect to AES (Advanced Encryption Standard) cipher described in Federal Information Processing Standards Publication 197, Announcing the ADVANCED ENCRYPT I/ON STANDARD (AES), Nov. 26, 2001, an implementation method described in Simplified Adaptive Multiplicative Masking for AES, Elena Trichina, Domenico De Seta, and Lucia Germani, LNCS 2523, p. 187-197 is known.